Kakashi's Strength Lies in His Speed, Attacks, Chakra(amount), and Jutsu that can all be preformed very quickly even a few feet away from your opponent. Also Moving with unpredictable movements makes him hard to sub. And with his Sharingan makes him and hard opponent to hit.
Kakashi's Weakness Lie in his medium range attacks which if too close to your opponent they can counter with an attack of their own before you get the chance to strike.
Stragieties with Kakashi:
1. Take advantage of His speed and quick jutsu charge, if and opponet is comming in hot and heavy back up and Jutsu them with a Lighting Blade. Or in Cases with faster character's Use Your Sharingan to protect you from their onslaught.
2. Kakashi is Strong make good use of Small hits they can turn into big combos and your opponent may find himself/herself losing more life than they espected.
3. Use your Sharingan, Especially against Lee, Gaara, and Haku as it can help deal with a barriage of his from Lee and Haku. But in the Case of Gaara can help out the Usually spammed Forward Y attack which can save your charka instead of subbing it. You could also try subbing his Forward Y and Grabbing him while he recovers.
Zabuza's Strengths are He is Extremely Stong, And can Desimate an Opponent in a few Combos. He has A Good Amount of Chakra, and has very good chakra control allowing you to use jutsu's pretty quickly.
Zabuza's Weakness are that he is Very Slow And his Move take time to do. which could leave you open to a counter attack. His Moves are also very perdictable.
Stragieties with Zabuza:
1. Stay a good 3 feet away because most of Zabuza's moves need a bit of a coushin to get off. Zabuza's Forward X Y X is a great Combo that will give you plenty of room, after the hit to get off a big jutsu LEVEL 2 or 3 your choice but if your not good at doing it I suggest using a Level 2 as it wastes less chakra.
2. When far from your opponent use his Back X Y attack as I will do some serious damage and Leave you plenty of room for a jutsu.
3. Down attacks work very well when opponent is getting up, also take advantage of Zabuza's grabs they are fast, and are strong, a nice trick that works with all characters is when your opponent is getting up try to time it so when they are standing you character grabs them.